An ash content and a calorific value are important property parameters of a coal, in which the calorific value of the coal may be computed by the ash content. Therefore, a technology for online measuring the ash content of the coal is of importance in a coal detection field. A traditional method for measuring the ash content of the coal generally uses a radiometric technology, such as a low-energy gamma ray back scattering method, a high-energy gamma ray electron pair effect, a natural gamma ray measuring method, a dual-energy gamma ray transmission method and a neutron activation prompt gamma analysis method.
The low-energy gamma ray back scattering method, the high-energy gamma ray electron pair effect, and the natural gamma ray measuring method are proved to be not suitable for measuring the ash content due to respective limitation, and thus they are not used widely.
The neutron activation prompt gamma analysis method can analyze element compositions of the coal, and then can measure the ash content and multiple different element contents of the coal according to the analysis. However, a device used for the neutron activation prompt gamma analysis method is very expensive. Moreover, a service life of a neutron source (such as californium-252) or a neutron tube used by the device is very short and needed to be regularly replaced, which further increase costs. In addition, a measuring accuracy of the neutron activation prompt gamma analysis method is actually not higher than that of the dual-energy gamma ray transmission method. Therefore, the neutron activation prompt gamma analysis method is not suitable for a large scale industrial application.
Currently, the dual-energy gamma ray transmission method is the most widely used method for measuring the ash content of the coal. Comparing to other methods above, the dual-energy gamma ray transmission method has advantages of being adapted for measuring coals with different particle sizes, thicknesses and densities. However, the measuring result of the dual-energy gamma ray transmission method is limited by the element compositions of the coal. In addition, the method uses a radioisotope as a radioactive source, which may do damage to an environment due to leakage during usage, transportation and decommission.